This invention relates to forming dies for forming bolts, nuts and similar machine parts.
Hitherto, in the forming of bolts, nuts and the like, a forming cavity has been formed in two adjacent parts, which parts were shrink-fitted within a reinforcement ring. In such prior devices, the two die parts were formed of super hard alloy and provided with a permanently open air flow hole extending into the die cavity at the interface of the parts. In such dies, however, it was found that the air vent passage was subject to being clogged with scale or oils from the workpiece. If the diameter of the vent hold was made large enough to avoid such clogging, the finished workpiece was found to have "flashes" resulting in an undesirable surface.
Also, such prior devices were customarily supported on a table meant to absorb the impact of the punch at the time of forming a workpiece. Those impacts were transmitted to the supporting table and a violent reaction force occurred in the dies which was found to often cause damage thereto.
It has also been proposed to support such dies on a compressive steel bed plate thereby absorbing impact by the elasticity of the bed plate. (Refer to "Punching Technique Handbook", pp 372; published on June 30, 1962; Publishers: Nikkan Kogyo Shimbun-sha. (Daily Industrial Newspaper Company, Ltd.), 1-1, Iida-cho, Chiyoda-ku, Tokyo, Japan).
In the above case, however, when the bed plate was compressed by the punching force of the punch, the following reaction often caused the upper die member to slip upwardly out of the reinforcing ring.